Shock waves, compression waves and so forth generated with the flow of air in, for example, characteristic sorting machines or appearance sorting machines that sort non-defective products and defective products using compressed air and manufacturing apparatuses employing compressed air actuators are a cause of noise.
Accordingly, there are noise reducing devices (sound reducers), such as the one disclosed in Japanese Unexamined Patent Application Publication No. 7-158418, for reducing noise generated with the flow of air.
As illustrated in FIG. 4, in Japanese Unexamined Patent Application Publication No. 7-158418, a sound reducer 150 is proposed in which a sound reducing case 101 is formed by providing a front cover 105 and a rear cover 106 at front and rear ends of a cylindrical body 104, an introduction port 105a through which a noise air flow is introduced is provided in the front cover 105, air flow lead out passages 106b are provided in the rear cover 106 and sound reduction is performed in a sound reducing chamber 107 formed inside the cylindrical body 104. In the sound reducer 150, part of the surface of the rear cover 106, the part of the surface facing the introduction port 105a, is an air flow reflecting surface 106a, the lead out passages 106b of the rear cover 106 are formed outside the reflecting surface 106a, first and second sound absorbing filters 108 and 109 are arranged at the entrance and exit of each lead out passage 106b and a space between the sound absorbing filters 108 and 109 serves as a sound reducing chamber 110.
This sound reducer is used by connecting gas discharged from a noise generating source 103 to the above-mentioned introduction port 105a using a discharge line (piping) 102.
However, when sound reduction is performed using the above-described noise reducing device (sound reducer) 150 having a configuration in which one introduction port (pipe connection portion) 105a and one sound reducing case 101 are provided, there is a problem in that the dimensions need to be made large in order to try and obtain a large sound reduction effect and it becomes difficult to arrange the noise reducing device close to the noise generating source 103 in such a case.
In addition, when attempting to reduce noise from an apparatus 103, which is a noise generating source having a plurality of discharge lines, by using a noise reducing device (sound reducer) provided with one introduction port (pipe connection portion) 105a and one sound reducing case 101 such as the noise reducing device (sound reducer) 150 of Japanese Unexamined Patent Application Publication No. 7-158418, it has been for example thought that noise reduction could be performed by first collecting the discharge lines 102a together using an integrating component 120 and then introducing the plurality of discharge lines 102a into the noise reducing device (sound reducer) 150 as schematically illustrated in FIG. 5. In this case, it would be necessary to use a noise reducing device (noise reducer) 150 having a sound reducing effect proportional to the number of discharge lines 102a. 
However, there is a problem in that discharge gas that has reached the integrating component 120 via the plurality of discharge lines 102a flows back into other discharge lines (for example, a discharge line that is not discharging discharge gas or a discharge line having a low pressure) 102a, the pressure in the discharge lines 102a into which discharge gas has flowed increases and the resistance to the discharge gas becomes high. When the discharge efficiency of the discharge lines 102a decreases due to the resistance to the discharge gas becoming high, there is a problem in that when the apparatus 130, which is a noise generating source, is a component sorting apparatus as described above for example, the apparatus 130 becomes unable to accurately sort non-defective products and defective products from each other.
Accordingly, a method has also been considered in which a check value (not illustrated) is provided in each of the discharge lines 102a in order to prevent the reverse flow (back flow) of the discharge gas into the discharge lines 102a as described above. However, if the ON-OFF operation frequency of the check values is high, the values undergo wear and the reliability of reverse flow prevention is degraded. Therefore, there is a problem in that a mechanism for checking a replacement period needs to be provided and the cost of providing the checking mechanism is incurred in addition to the cost of providing the check valves.
In addition, there is a problem in that it is considered that a configuration must be adopted in which the use period is used as a criterion in order that a check valve can be replaced before the reverse flow prevention function is degraded and therefore the economic burden is increased in this case.
Furthermore, a method has also been considered in which noise is reduced by installing a noise reducing device for each of the plurality of discharge lines 102a, but a large-size noise reducing device capable of obtaining a sufficient sound reduction effect would have to be installed for each of the plurality of discharge lines 102a in order to obtain a sufficient sound reduction effect and therefore space is needed. If a small-size noise reducing device was installed for each of the plurality of discharge lines 102a, although the installation space would be small, there would be a problem in that the sound reduction effect would be insufficient.